Method of treating HIV with 2&#39;,3&#39;-dideoxyinosine

ABSTRACT

A method for tearing retroviral infections including acquired immune deficiency syndrome (AIDS) with 2&#39;,3&#39;-dideoxyinosine or 2&#39;,3&#39;-dideoxyadenosine is disclosed. This antiviral effect is irreversible with 2&#39;,3&#39;-dideoxyinosine and 2&#39;,3&#39;-dideoxyadenosine but reversible with 2&#39;,3&#39;-dideoxyguanosine.

This application is a continuation of Ser. No. 07/420,664, filed Aug.28, 1989, abandoned; which is a continuation of Ser. No. 07/084,055filed Aug. 11, 1987, now U.S. Pat. No. 4,861,759; which is acontinuation-in-part of application Ser. No. 06/937,925, filed Dec. 4,1986, abandoned; which is a continuation-in-part of application Ser. No.07/769,016 filed Aug. 26, 1985, abandoned, each of which is incorporatedby reference in its entirety.

The present invention relates to a method of treatment to preventcytopathic effects of viruses. Of particular concern is protectionagainst the cytopathic effects of HTLV/LAV virus (now known as humanimmunodeficiency virus (HIV)), the causative agent of acquired immunedisease syndrome (AIDS), and its related disorders. Both parenteral useand oral use are described.

BACKGROUND OF THE INVENTION

The HIV virus which causes AIDS exerts a profound cytopathic effect onthe helper/inducer T-cells, devastating the function of the immunesystem. The virus also shows a propensity to infect the brain withresulting neurological deterioration. The disease results in progressivedebilitation and death.

While several antiviral agents have been tested for use as a treatmentof AIDS patients, no fully satisfactory antiviral agent has been found.See, for example:

Mitsuya, H. et al. Science, 226, 172-174 (1984)

Broder, S. AIDS: Modern Concepts and Therapeutic Challenges. MarcelDekker, Inc., New York 1987

Rosenbaum, W. et al. Lancet, i, 450-451 (1985)

McCormick, J.B., Getchell, J.P., Mitchell, S.W., & Hicks, D. R. Lancet,ii, 1367-1369 (1984)

Ho, D.D. et al. Lancet, i, 602-604 (1985)

Sandstrom, E.G., Kaplan, J.C., Byington, R.E., & Hirsch, M.S. Lancet, i,1480-1482 (1985)

Azidothymidine (AZT) is presently being used for treatment, but theserious toxic side reactions, and high cost of therapy present seriouschallenges in continued use for many patients.

SUMMARY OF THE INVENTION

It is an object of the invention to provide therapeutic compositions andmethods of treatment which overcome the deficiencies of the prior artcompositions and methods of treatment cited above.

It is, furthermore, the object of the present invention to providecompositions and methods of treatment which may be useful in treatingpatients with viral infections, particularly for treatment of AIDSpatients.

It is a further object of the invention to provide means forintracellular delivery of the phosphorylated nucleosides to infectedcells.

While the exact mechanism of antiviral activity of the compositions ofthe present invention is unknown, the probable mechanism involvesmodifying the naturally occurring 3'-carbon of the deoxyribose (of theviral RNA) so that it is not possible to form 5'-- 3'phosphodiesterlinkages necessary for DNA elongation in the replication of the virusfrom an RNA form to a DNA form. Once the drug enters a cell it isconverted to a triphosphate. The 2',3'-dideoxynucleoside purines whichhave been converted to triphosphates by cellular enzymes, are used intranscription instead of 2'-deoxynucleoside-5'-triphosphate. The2',3'-dideoxynucleoside triphosphates act as DNA chain terminators, thusinhibiting DNA synthesis mediated by HIV reverse transcriptase and/or itcan act by competitively inhibiting the binding of the natural substratefor reverse transcriptase.

One embodiment of the present invention involves the direct delivery ofthe triphosphate derivative to the host cells. It is well known bypractitioners in the art that "unshielded" triphosphates cannot be usedas drugs because triphosphate compounds do not penetrate cell membranes.Accordingly, the triphosphate derivatives of this invention may bedelivered by means of liposomes, small particles (about 25 uM to 1 uM indiameter) which serve as intracellular transport systems to delivernormally nonabsorbable drugs across the cell membrane. The use ofliposomes for drug delivery is well known in the art and is based on aphospholipid's ability to spontaneously form bilayers in aqueousenvironments. One method of forming liposomes is by agitatingphospholipids in aqueous suspensions at high frequencies; this resultsin the closed vesicles characteristic of liposomes. Once inside thecells, the triphosphate derivatives act, as noted above, in thesuppression of the cytopathic effects of HIV. The use of a liposomedelivery system is clearly indicated as particularly appropriate basedon our data indicating the triphosphate form is the drug that is activeinside the cell.

In the specification and claims a so-called "safe" use is noted and isdefined as the use of a treating agent in a concentration sufficient tosuppress viral replication, but lower than the concentration which willharm the host cell.

MATERIAL INFORMATION DISCLOSURE

Furmanski et al., "Inhibition by 2',3'-Dideoxythymidine of RetroviralInfection of Mouse and Human Cells," Cancer Letters, 8:307-315, 1980.

Wagar et al., "Effects of 2',3'-Dideoxynucleosides on Mammalian Cellsand Viruses," Journal of Cellular Physiology, 121:402-408 (1984).

SPECIFIC DESCRIPTION OF THE INVENTION Active Ingredient

The compositions of the present invention comprise purine nucleosideswith the ribose moiety of the molecule in the 2',3'-dideoxyconfiguration, and a pharmaceutically acceptable carrier. In thepreferred embodiment, the active ingredient is 2',3'-dideoxyinosine,2',3'-dideoxyguanosine, or 2',3'-dideoxyadenosine, illustrated below:##STR1##

Preferred esters of the compounds of the formulas include carboxylicacid esters in which the non-carbonyl moiety of the ester grouping isselected from straight or branched chain alkyl, alkoxyalkyl (e.g.,methoxymethyl), aralkyl (e.g., benzyl), aryloxyalkyl (e.g.,phenoxymethyl), aryl (e.g., phenyl optionally substituted by halogen,C₁₋₄ alkyl or C₁₋₄ alkoxy); sulphonate esters such as alkyl- oraralkylsulphonyl (e.g., methanesulphonyl); and mono-, di- ortriphosphate esters.

Any reference to the above-described compounds also includes a referenceto a pharmaceutically acceptable salt thereof with regard to theabove-cited derivatives. Unless otherwise specified, any alkyl moietypresent advantagenously contains 1 to 18 carbon atoms, particularly 1 to4 carbon atoms. Any aryl moiety present in such esters advantageouslycomprises a phenyl group, including a substituted phenyl group.

Examples of pharmaceutically acceptable salts of the compounds offormula (1) and pharmaceutically acceptable derivatives thereof includebase salts, e.g., derived from an appropriate base, such as alkali metal(e.g., sodium), alkaline earth metal (e.g., magnesium) salts, ammoniumand NX₄ (wherein X is C₁₋₄ alkyl). Physiologically acceptable saltscontaining a hydrogen atom or an amino group include salts of organiccarboxylic acids such as acetic, lactic, tartaric, malic, isothionic,lactobionic and succinic acids; organic sulfonic acids such asmethanesulfonic, ethanesulfonic, benzenasulfonic and p-tolunesulfonicacids and inorganic acids such as hydrochloric, sulfuric, phosphoric andsulfamic acids. Physiologically acceptable salts of a compoundcontaining any hydroxy group include the anion of said compound incombination with a suitable cation such as Na⁺, NHY₄ ⁺, and NX₄ ⁺(wherein X is a C₁₋₄ alkyl group).

Specific examples of pharmaceutically acceptable derivatives of thecompound of the formulas that may be used in accordance with the presentinvention include the monosodium salt and the following 5' esters;monophosphate; disodium monophosphate; diphosphate; triphosphate;acetate; 3-methyl-butyrate; octanoate; palmitate; 3-chloro benzoate;benzoate; 4-methyl benzoate; hydrogen succinate; pivalate; and mesylate.

Also included within the scope of this invention are thepharmaceutically acceptable salts, esters, salts of such esters, nitrileoxides, or any other covalently linked or non-linked compound which,upon administration to the recipient, is capable of providing (directlyor indirectly) a nucleoside analog as described above, or ananti-virally active metabolite or residue thereof. All of thesecompounds are active and relatively non-toxic at concentrations ofsufficient potency for effective Inhibition of viral infectivity andreplication.

Pharmaceutically Acceptable Carrier

It is possible for the nucleoside of the present invention to beadministered alone in solution. However, in the preferred embodiment,the active ingredient(s) may be used or administered in a pharmaceuticalformulation. These formulations comprise at least one active ingredient(the nucleoside), together with one or more pharmaceutically acceptablecarriers and/or other therapeutic agents. As included within the scopeof this invention, "acceptable" is defined as being compatible withother ingredients of the formulation and non injurious to the patient orhost cell. These carriers include those well known to practitioners inthe art as suitable for oral, rectal, nasal, topical, buccal,sublingual, vaginal, or parenteral (including subcutaenous,intramuscular, intravenous, and intradermal) administration. Specificcarriers suitable for use in the Invention are further defined below.

In general, a suitable dose is in the range of 1.0 to 120 mq perkilogram body weight per day and most preferably in the range 10 to 60mg per kilogram body weight per day. The desired dose is provided inseveral increments at regular intervals throughout the day by continuousinfusion or sustained release formulations. The doses will need to bemodified according to the patients hepatic, renal, and bone marrowfunction, functions which are frequently abnormal in patients withadvanced retroviral infections.

Ideally, the active ingredient is administered to achieve peak plasmaconcentrations of the active compound of from about 0.5 uM to about 50uM, and preferably about 1 to 30 uM. This may be achieved, for example,by the intravenous injection of 0.1% to 50% concentration in solution ofthe active ingredient or may be administered orally in doses of about 1to about 100 mg/kg of the active ingredient. Desirable blood levels maybe maintained by a continuous infusion to provide about 0.01 to about5.0 mg/kg/hour or by intermittent infusions containing about 0.4 toabout 16 mg/kg of the active ingredient. Ideally, concentrations in thecerebrospinal fluid should reach 10-100% of the circulating plasmaconcentrations. This may be achieved by systemic or intrathecaladministration.

The 2',3'-dideoxynucleosides may be administered orally in liquid or intablet form, and may include one or more of the following: lactose(hydrous, fast flow), microcrystalline cellulose, colloidal silicondioxide, croscarmellose sodium, magnesium stearate, stearic acid, andother excipients, colorants, and pharmacologically compatible carriers.Compositions for oral use may be administered to patients in fasting andnon-fasting states.

Formulations of the present invention suitable for oral administration(including sustained release formulations) may be presented as discreteunits such as capsules, cachets or tablets, each containing apredetermined amount of the active ingredient; as a powder or granules;as a solution or a suspension in an aqueous liquid; in an oil-in-waterliquid emulsion or a water-in-oil liquid emulsion. The active ingredientmay also be presented as a bolus, electuary or paste.

Tablets may optionally be provided with an enteric coating, to providerelease in parts of the gut other than the stomach.

Formulations suitable for topical administration in the mouth includelozenges comprising the active ingredient in a flavor, usually sucroseand acacia or tragacanth; pastilies comprising the active ingredient inan inert basis such as gelatin and glycerin, or sucrose and acacia; andmouthwashes comprising the active ingredient in a suitable liquidcarrier.

Formulations for rectal administration may be presented as a suppositorywith a stiltable base comprising, for example, cocoa butter or asalicylate.

Formulations suitable for vaginal administration may be presented aspessaries, tampons, creams, gels, pastes, foams, or spray formulascontaining in addition to the active ingredient such carriers as areknown in the art to be appropriate.

Formulations suitable for parenteral administration include aqueous andnon-aqueous, isotonic sterile injection solutions which may containantioxidants, buffers, bacteriostats and solutes which render theformulation isotonic with the blood of the intended recipient; andaqueous and non-aqueous sterile suspensions which may include suspendingagents and thickening agents. The formulations may be presented inunit-dose or multi-dose sealed containers, for example, ampules andvials, and may be stored in a freeze-dried (lyophilized) conditionrequiring only the addition of the sterile liquid carrier, for example,water for injections, immediately prior to use. Extemporanenousinjection solutions and suspensions may be prepared from sterilepowders, granules and tablets of the kind previously described.

As previously indicated, it Is highly desirable to administermedications by oral route when long-term treatment is required. Sincethe instantly claimed compounds are not stable within the acid range, itis necessary, in order to provide acceptable bioavailability, to bufferthe compositions to obtain a composition in the neutral (pH 6-pH 8)range. At about pH 7 the bioavailability increases greatly so that oraladministration of the nucleosides becomes practicable.

The antiviral agents of the invention may be used in conjunction withother antiviral drugs or antibiotics. Immune modulating therapyincluding bone marrow or lymphocyte transplants may be usedconcurrently.

DETAILED DESCRIPTION OF THE DRAWINGS

In FIG. 1a-1e, which shows the survival and growth of human ATH8 cellsin the presence of 2',3'-dideoxynucleosides when exposed to HIV(HTLV-III/LAV), 2×10⁵ ATH8 cells were treated with polyrene, exposed toHTLV-III₈ (2,000 virus particles/cell), resuspended in culture tubes,and cultured (solid symbols) in the absence of drugs (FIG. 1a); or inthe presence of 50 uM 2',3'-dideoxyadenosine (Calbiochem-Behring Corp.,LaJolla, Calif.) (FIG. 1b); in the presence of 50 uM2',3'-dideoxyinosine (Calbiochem-Behring Corp.) (FIG. 1c); in thepresence of 1 uM 2',3'-dideoxycytidine (Calbiochem-Behring Corp.) (FIG.1d); and in the presence of 500 uM 2',3'-dideoxythymidine (P.L.Biochemicals Inc., Milwaukee, Wis.) (FIG. 1e). Control cells weresimilarly treated but were not exposed to the virus (open symbols). Atvarious time points, total viable cells were counted as describedExample 1.

In FIG. 2a-2e, which show the inhibition of cytopathic effect of HIV(HTLV-III/LAV) by various 2',3'-dideoxynucleosides against target ATH₈cells, 2×10⁵ ATH8 cells were preexposed to polybrene, exposed toHTLV-III_(B) (2,000 virus particles/cell) in culture tubes (solidcolumns) in the presence or absence of various concentrations of2',3'-dideoxyadenosine, 2',3'-dideoxyinosine, 2',3'-dideoxyguanosine(P.L. Biochemicals Inc.), 2',3'-dideoxycytidine, or2',3'-dideoxythymidine. Control cells (open columns) were similarlytreated but were not exposed to the virus. On day 5, total viable cellswere counted as described in Example 1.

In FIG. 2f-2j which shows the inhibition of the infectivity andreplication of HIV (HTLV-III/LAV) in H9 cells by various2',3'-dideoxynucleosides, 10⁵ H9 cells were exposed to variousconcentrations of 2',3'-dideoxynucleosides for 4 hours, then to 2 ug/mlpolybrene for 30 minutes, pelleted, and exposed to HTLV-III_(B) (3,000virus particles/cell) for 1.5 hours. Cells were resuspended in freshcomplete medium and cultured in tubes at 37° C. in 5% CO₂ -containinghumidified air. The cells were continuously exposed to2',3'-dideoxynucleosides. On days 8 (left), 9 (middle), and 10 (right)in culture, the percentage of the target H9 cells expressing p24 gagprotein of HIV (HTLV-III/LAV) was determined by indirectimnunofluorescence microscopy by using anti-HIV p24 murine monoclonalantibody (M26 provided by Drs. F.D. Veronese and R.C. Gallo).

In FIG. 2k-2o, which show protection (or lack of protection) of ATH8cells by various adenosine congeners against the cytopathic effect ofHIV (HTLV-III/LAV), 2×10⁵ ATH8 cells were preexposed to polybrene,exposed to HTLV-III_(B) (2,000 virus particles/cell), resuspended inculture tubes (solid columns) in the presence or absence of variousamounts of adenosine congeners: 2',3'-dideoxyadenosine (2k);2'-deoxyadenosine (Calbiochem-Behring Corp.) (2l); 3'-deoxyadenosine(cordycepin; Behringer-Mannheim GmbH, West Germany) (2m); adenosinearabinoside (2n); and 2',3',5'-trideoxyadenosine (2o) (both provided byDrs. D. Johns, J. Driscoll, and G. Milne). The primed numbers in (2k)refer to positions in the sugar moiety. Control cells (open columns)were not exposed to the virus. On day 5, the total viable cells werecounted as described in Example 1.

SPECIFIC DESCRIPTION OF THE PROCESS

In the system, HIV (HTLV-III/LAV) (as cell-free virus) exerts a profoundcytopathic effect on the target T-cells by day 4 in culture, and by day10, >98% of the cells are killed by the virus (FIG. 1-a). The killing ofcells can be monitored quantitatively as a function of the starting doseof virus (Table 1). When ATH8 cells are used in a 7-day assay, 5 virusparticles/cell represented the minimum cytopathic dose of virus. In theexperiments reported below, 2,000 or 3,000 virus particles/cell wereused in order to test various compounds under conditions of substantialvirus excess.

FIG. 1 (b-e) and FIG. 2a-2e illustrate the protective effect of ie2',3'-dideoxynucleosides on the survival and growth of ATH8 cells whenexposed to HIV (HTLV-III/LAV). In the present experimental conditions,2',3'-dideoxythymidine required relatively high concentrations to exerta protective effect, and unlike the other comparable dideoxynucleosidestested, its capacity to nullify the cytopathic effect of the virus waslost on day 10 of the culture (FIG. 1-3 75 FIG. 2- ). It is not possibleto deduce which compounds will work against HIV and be non-toxic forhuman cells from first principles or the prior art.

These anti-viral effects were confirmed in a different system, using theexpression of the HIV (HTLV-III/LAV) p 24 gag protein in H9 cells (FIGS.2f-2j). The H9 cells are relatively resistant to the cytopathic effectof HIV (HTLV-III/LAV), and p24 gag protein expression following exposureto virions may be used as an index of viral infectivity and replicationin vitro. Again, 2',3'-dideoxythymidine required relatively higherconcentrations to mediate an anti-viral effect, and this compoundallowed a resumption of viral replication by day 10 of culture (FIG. 2j)Each drug must, therefore, be evaluated in its own right.

There was tested the effects of the various 2',3'-dideoxynucleosides onthe antigen-specific and lectin-induced reactivity of normal lymphocytesin vitro (Table 2). There was used a normal clone (TM3) oftetanus-toxoid specific helper/inducer T-cells to monitor the effects ofthe compounds on antigen-driven activation and normal circulatinglymphocytes to monitor effects on pokeweed mitogen andphytohaemagglutinin-driven activation. Concentrations of thesecompounds, including those that were 10- to 20-fold higher than thosenecessary to block the in vitro infectivity and cytopathic effect of HIV(HTLV-III/LAV) left the in vitro immune reactivity of normal lymphocytesbasically intact.

The mechanisms by which 2',3'-dideoxynucleosides suppress thereplication of HIV (HTLV-III/LAV) are not fully known. It is known thatthe 5'-triphosphate product of 2',3'-dideoxyadenosine,-dideoxyguanosine, and -dideoxyadenosine can inhibit cellular DNApolymerases beta and gamma, as well as viral reverse transcriptase (videinfra), but not mammalian DNA polymerase alpha. DNA polymerase alpha isassumed to be the key DNA synthetic enzyme for DNA replication duringcell division, and it also has a role in DNA repair. Of interest, Herpessimplex type I DNA polymerase is reported to be as resistant to2',3'-dideoxythymidine as cellular DNA polymerase alpha.Unphosphorylated dideoxynucleosides have rather negligible effects onthe growth of cultured mammalian cells (a phenomenon which is confirmedhere in human T-cells). This is believed to be so because ofcomparatively inefficient intracellular conversion to the corresponding5'-triphosphates coupled with the resistance of DNA polymerase alpha tolow levels of the 5'-triphosphaths.

EXAMPLE 1

With reference to Table 1, a human tetanus toxoid-specific T-cell line,established by repeated cycles of stimulation with antigen as describedin Mitsuya et al., Science, 225:1484-1486 (1984), was cloned in thepresence of lethally irradiated (12,000 rad) human T-lymphotropic virustype I (HTLV-I)-producing MJ-tumor cells in 96-well microtiter cultureplates (Costar, Cambridge, Mass.). Clone ATH8 (obtained from a cultureplated at 0.5 cells per well) was selected for drug screening on thebasis of its rapid growth (in the presence of interleukin-2) andexquisite sensitivity in vitro to the cytopathic effect of HIV(HTLV-III/LAV). ATH8 clone bears several distinct copies of HTLV-I inits genome when assessed by Southern blot hybridization using aradiolabelled HTLV-I cDNA probe but does not produce detectable amountsof HTLV-I p24 ml protein. 10⁵ ATH8 cells were preexposed to 2 ug/mlpolybrene for 30 minutes, pelleted, exposed to various amounts ofHTLV-III_(B), resuspended in 2 ml complete medium (RPMI supplementedwith 15% undialysed, heat-inactivated fetal calf serum, 4 mML-glutamine, 5×10⁻⁵ 2-mercaptoethanol, 50 U/ml penicillin, and 50 ug/mlstreptomycin) containing 15% (vol/vol)-interleukin 2 (lectin-depleted;Cellular Products Inc., Buffalo, N.Y.), and incubated in culture tubes(3033, Falcon, Oxnard, Calif.) at 37° C. in 5% CO₂ -containinghumidified air. On day 7, the total viable cells were counted by thetrypan blue dye exclusion method. Table 1 shows the cytopathic effect ofHIV (HTLV-III/LAV) on the ATH8 cells; data are expressed as thearithmetic means+1 standard deviation for duplicate determinations.

                  TABLE 1                                                         ______________________________________                                        Cytopathic Effect of HTLV-III/LAV on ATH8 Cells                               Number of HTLV-III.sub.B                                                                       Number of Viable                                             Virus Particles/Cell                                                                           ATH8 Cells (× 10.sup.5)                                ______________________________________                                        0                3.37 ± 0.1                                                0.05             3.36 ± 0.04                                               0.5              3.26 ± 0.15                                               5                1.97 ± 0.2                                                50               1.78 ± 0.16                                               500              0.37 ± 0.02                                               5,000            0.30 ± 0.01                                               ______________________________________                                    

                                      TABLE 2                                     __________________________________________________________________________    Effect of 2',3'-Dideoxynucleosides on the in vitro Immune Reactivity of       Normal Lymphocytes                                                            Responder   Adenosine.sup.1                                                                         Guanosine.sup.1                                                                         Inosine.sup.1 Cytidine.sup.4                                                                         Thymidine.sup.4        Cells  None 10   100  10   100  10   100  None.sup.4                                                                        1    10  200 2,000              __________________________________________________________________________    C1 TM3.sup.2                                                                         75 ± 6                                                                          86 ± 8                                                                          67 ± 2                                                                          66 ± 5                                                                          77 ± 1                                                                          62 ± 4                                                                          81 ± 4                                                                          12 ± 1                                                                         13 ± 1                                                                           8 ± 1                                                                          9                                                                                 9 ± 1          PBM +  310 ± 39                                                                        289 ± 18                                                                        314 ± 37                                                                        350 ± 4                                                                         469 ± 9                                                                         298 ± 20                                                                        355 ± 37                                                                        82 ± 1                                                                         101 ± 1                                                                         86 ± 3                                                                         86                                                                                77 ± 8          PHA.sup.3                                                                     PBM +  63 ± 2                                                                          63 ± 5                                                                          57 ± 3                                                                          73 ± 8                                                                          62 ± 5                                                                          61 ± 1                                                                          62 ± 5                                                                          24 ± 1                                                                         23 ± 3                                                                          15 ± 3                                                                         31                                                                                31 ± 1          PWM.sup.3                                                                     __________________________________________________________________________     .sup.1 All nucleosides tested are of 2',3dideoxy-configuartion.               Concentrations (uM) of each 2',3dideoxynucleoside bring about virtually       complete inhibition of the cytopathic effect of HTLVIII/LAV (FIGS. 1 and      2a) and the viral p24 expression (except 2',3dideoxythymidine; see FIG.       2b). .sup.3 Hthymidine incorporation was used as an indicator of              activation of responder cells (vide infra), unless otherwise indicated.       .sup.2 5 × 10.sup.4 normal helper/inducer TM3 cells were stimulated     with tetanus toxoid (0.6 limiting flocculation units/ml) plus 10.sup.5        irradiated (4,000 rad) autologous peripheral blood mononuclear cells (PBM     as a source of accessory cells and cultured for 72 hours in the presence      or absence of the 2',3dideoxynucleoside. After exposure to 0.5 uCi .sup.3     Hthymidine or 1 uCi .sup.3 Huridine for the final 5 hours, cells were         harvested onto glass fibers and the incorporated radioactivity was            counted. Data are expressed as the arithmetic mean counts per minute          (× 10.sup.3) ± 1 standard deviation triplicate determinations.       .sup.3 10.sup.6 PBM from a healthy individual were stimulated with            phytohaemagglutinin (PHA) or pokeweed mitogen (PWM) and culture for 72        hours and treated as described above.                                         .sup.4 .sup.3 Huridine incorporation was used as an indicator of              activation of the responder cells.                                       

EXAMPLE 2

Beagle dogs were administered 500 mg/kg bodyweight of2',3'-dideoxyadenosine (ddA) as either a short (15 minutes) intravenousinfusion in saline, or as an oral gavage in 0.1N acetate buffer (pH7.0). Drug concentration in both solutions was 25 mg/ml, whichnecessitated the administration of about 300 ml of solution by eitherroute. Oral bioavailability was calculated for dideoxyinosine (theplasma product of dideoxyadenosine) based on the ddA dose. Oralbioavailability was calculated to be 41.6% with the orally administeredddA was converted almost entirely to 2',3'-dideoxyinosine (ddl). BothddA and ddl have anti-retroviral activity against HIV. FIG. 3 shows ddIconcentration up to 500 minutes after oral administration of ddA.

EXAMPLE 3

The antiviral activity of the dideoxynucleosides of the presentinvention against a variety of viruses were compared. The results, shownin Table 3, indicate that the compositions of the present invention areselectively effective against HIV virus.

                                      TABLE 3                                     __________________________________________________________________________    Antiviral Activity of 2',3'-Dideoxynucleosides                                                 Minimal Inhibitory Concentration (uM).sup.1                                   Dideoxy-                                                                           Dideoxy-                                                                            Dideoxy-                                                                           Dideoxy-                                     Virus            uridine                                                                            thymidine                                                                           adenosine                                                                          cytidine                                     __________________________________________________________________________    DNA virus                                                                           HSV-1.sup.2                                                                              .sup. >2,000.sup.6                                                                 >2,000                                                                              >2,000                                                                             >2,000                                             HSV-1.sup.2                                                                              >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Vaccinia.sup.2                                                                           >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                       RNA virus                                                                           Vesicular Stomatitis                                                                     >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Virus.sup.2,3                                                                            >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Reovirus-1.sup.4                                                                         >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Sindbis Virus.sup.4                                                                      >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Coxsackie Virus B4.sup.3                                                                 >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Semliki Forest Virus.sup.4                                                               >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Parainfluenza Virus-3.sup.4                                                              >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                             Polio Virus-1.sup.3                                                                      >2,000                                                                             >2,000                                                                              >2,000                                                                             >2,000                                       Retrovirus                                                                          HTLV-III.sup.5                                                                             >100                                                                                200                                                                                  5                                                                                0.3                                        __________________________________________________________________________     .sup.1 Required to reduce virusinduced cytopathogenicity by 50%.              .sup.2 Antiviral activity measured in primary rabbit kidney cell cultures     .sup.3 Antiviral activity measured in Hela cell cultures.                     .sup.4 Antiviral activity measured in Vero cell cultures.                     .sup.5 Antiviral activity measured in T4.sup.+  human T cell (ATH8)           cultures.                                                                     .sup.6 A value >2,000 denotes that at concentration of up to 2,000 uM the     nucleoside failed to inhibit the specified virus.                             Note:                                                                         2',3dideoxyadenosine and 2',3dideoxycytidine were not active against the      broad spectrum of DNA and RNA viruses shown above, except that they were      active against HIV the human HTLVIII (AIDScausing) virus.                

What is claimed is:
 1. A method for treating an individual infected withhuman immunodeficiency virus, comprising administering a therapeuticallyeffective amount of 2',3'-dideoxyinosine or a pharmaceuticallyacceptable salt thereof, to said individual.
 2. The method according toclaim 1 wherein the therapeutically effective amount of2',3'-dideoxyinosine is administered orally.
 3. The method according toclaim 1 wherein the therapeutically effective amount of2',3'-dideoxyinosine is administered intravenously.
 4. The methodaccording to claim 1 wherein the therapeutically effective amount of2',3'-dideoxyinosine is administered intramuscularly.
 5. The methodaccording to claim 1 wherein the therapeutically effective amount of2',3'-dideoxyinosine is administered subcutaneously.
 6. The methodaccording to claim 1 wherein the 2',3'-dideoxyinosine is administered tothe individual to achieve peak plasma concentrations ranging from about0.5 uM to about 50 uM.
 7. The method according to claim 1 in which the2',3'-dideoxyinosine is administered to the individual to achieve peakplasma concentrations ranging from about 1 uM to about 30 uM.